(a) Field of the Invention
The present invention relates to a power factor correction circuit, and a driving method thereof.
(b) Description of the Related Art
A power factor indicates effectiveness of power transmission. In transmission of power, actually transmitted power is real power. The power factor is shown by dividing real power by apparent power that is a product of real values of voltage and current of power. In this instance, when the voltage and the current are sine waves, the power factor is changed by a phase difference between the voltage and the current. The power factor is improved as the phase difference is reduced. Therefore, general power factor compensation for improving the power factor represents an operation for correcting a shape of an input current to be a sine wave shape and reducing a phase difference between the voltage and the current.
A conventional power factor correction circuit full-wave rectifies input AC power to generate an input voltage, and controls an inductor current to have a phase and a frequency close to the input voltage. The input current of the power factor correction circuit is a value generated by eliminating the radio frequency component from the inductor current by using a predetermined low-pass filter.
FIG. 11 shows an inductor current of a power factor correction circuit. As shown in FIG. 11, the inductor current has a sawtooth shape, and peak values have a sine wave shape shown by a dotted line. As shown in FIG. 11, the inductor current is filtered to generate a smooth input current shown with a thick solid line.
The power factor correction circuit controls the inductor current by controlling a switching operation of a switch connected to an inductor. Since the input current is determined according to the inductor current, the power factor correction circuit controls the input current by controlling the switching operation. Information on the input voltage may not be needed according to a method for driving the power factor correction circuit. In detail, a critical conduction mode power factor correction circuit (PFC) generates the inductor current and the input current shown in FIG. 11. The critical conduction mode power factor correction circuit uses the current and output voltage flowing to the switch to control the switching operation of the switch. Therefore, no additional input voltage information is required.
In general, a control circuit for controlling the power factor correction circuit is realized as a chip, and the existing control circuit chip includes an additional pin for receiving the input voltage. The existing control circuit chip uses a resistor for sensing the input voltage, but the resistor causes power consumption.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.